How to build PostGIS database schema for flexibility and normalization?

I'm creating a database that will be used by researchers in population genetics with different goals and sampling strategies. The database needs to accommodate locations as points, lines, or polygons and I'm puzzling over whether those should be kept in a single "locations" table, or in separate tables for "point_locations", "line_locations", and "polygon_locations". The single-table design is appealing because it would make it simple to enforce the required one-to-one relationship between samples and their locations with a foreign key constraint. I can imagine that there may be reasons to split locations out into separate tables for points, lines, and polygons, however. If I can keep all locations' spatial data in a single column, then which geography datatype should I use (I know geometry would be more flexible, but that's a topic for another post)? I'm thinking geography(polygon,4326).